The invention relates to orthopedic devices in aid of bone-fracture repair and, in particular, to a patient-operated device for stimulated transient distraction of fractured components of a bone.
External fixators of the nature disclosed in U.S. Pat. Re. 31,809 and 4,621,627 rely upon an elongate central body of selectively adjustable length, with a bone-screw or bone-pin anchoring clamp at each longitudinal end of the body, with preferably a selectively locked ball-joint connection between each anchoring clamp and the body end to which it is connected. Selectively available body length involves telescoping body parts which are keyed against rotation and which can be secured to each other to hold a given setting of longitudinal span between the anchoring clamps. Provision is made for periodic precision increments of length to be made in the clamped relation of the telescoping body parts, by employing a length-adjusting jacking mechanism which may be an accessory device used by the surgeon to periodically adjust overall fixator-body length, in the course of a number of weeks of healing repair of the fracture; the accessory device is detachably applicable-to the respective fixator-body parts, for incrementally jacking the fixator-body parts while momentarily releasing the secured relation of these body parts, the secured condition of the body parts being re-established before detaching the jacking mechanism.
In the course of normal leg fracture repair with such fixators, there is a period of several weeks during which the fixator-braced fracture is subjected to weight-bearing, i.e., the patient must stand and learn to walk with the clamped fixator. At the outset of this period, the fixator (via its bone-screw or bone-pin anchorages) takes almost all of the patient's body weight, and in the ensuing course of time the fidelity of bone-screw or bone-pin anchorage to the fractured bone gradually degrades, thus causing the healing bone to assume an increasing fraction of transient weight-bearing loads, as when walking. The nature of such transient loads is one of transient compressional loading of the fracture, which has been identified as a therapeutic aid that enhances the strength and the speed of bone repair, with shortened duration of the period of the patient's need for his fixator.
Recognition of the therapeutic value of periodic transient compression during the weight-bearing phase of bone-fracture repair has given rise to various modifications of external-fixator construction, so as to provide for more control of transient compressional loading. Such devices are sometimes called dynamic axial fixators, as in the case of U.S. Pat. No. 5,320,622. Other forms of such devices are disclosed in Sturtzkopf, et al. U.S. Pat. No. 5,026,372 and in Harris, et al. U.S. Pat. No. 4,502,473.
Applicant has discovered that therapy involving transient distraction of a fracture is accompanied by callus development at the fracture site, to an extent which exceeds and which is superior to that resulting from transient compression associated with or in replication of the weight-bearing phenomenon discussed above. Moreover, therapy involving transient distraction has no relation or analogy to weight-bearing, and applicant has found that transient distraction therapy does not require that the patient shall yet have progressed to the weight-bearing phase of fracture repair.